MB-12643:bp:MB-12156 Don't delete buckets when changing datapath.

Change-Id: I0039e0bfa7353cd784791e6f7aca7d73a89778b7
Orig-Reviewed-on: http://review.couchbase.org/41332
Reviewed-on: http://review.couchbase.org/43229
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>